Covalent Bonding

Covalent Bonding

Covalent bonding happens when non-metal atoms share electrons to achieve a full outer shell. It forms molecules, not ions.

 

What is a covalent bond?

A covalent bond is a shared pair of electrons between two non-metal atoms.

  • Each atom contributes at least one electron to the shared pair
  • No electrons are transferred
  • This bond is strong and holds the atoms together in a molecule
  •  

Why do atoms form covalent bonds?

  • Non-metal atoms have 5, 6 or 7 outer electrons
  • They cannot lose electrons easily (unlike metals)
  • So they share electrons to complete their outer shell and become stable
 

Examples of simple covalent molecules

Molecule

Atoms involved

Bonding

Electron pairs shared

H₂

2 hydrogen

Single bond (H–H)

1

Cl₂

2 chlorine

Single bond (Cl–Cl)

1

H₂O

2 hydrogen + oxygen

2 single bonds (H–O–H)

2 (1 per H)

CH₄

1 carbon + 4 hydrogen

4 single bonds

4

O₂

2 oxygen

Double bond (O=O)

2

N₂

2 nitrogen

Triple bond (N≡N)

3

Dot and cross diagram descriptions

  • Oxygen: two atoms, each with six outer electrons
  • Two pairs of electrons shared (double bond)
  • Remaining electrons shown as lone pairs
  •  

Properties of simple covalent molecules

  • Low melting and boiling points – weak intermolecular forces between molecules
  • Don’t conduct electricity – no free electrons or ions
  • Usually gases or liquids at room temperature

💡 The covalent bonds inside molecules are strong, but the forces between molecules are weak.

 

Larger covalent structures

Some covalent substances form giant covalent structures, not simple molecules.
These include:

  • Diamond – each carbon makes 4 bonds, very hard, high melting point
  • Graphite – each carbon makes 3 bonds, layers slide, conducts electricity
  • Silicon dioxide (SiO₂) – found in sand, strong structure, high melting point
 

These have very high melting points due to strong covalent bonds throughout the structure.

Questions 

  1. What types of atoms form covalent bonds?
  2. How many electrons are in a shared pair?
  3. Why do simple covalent molecules have low boiling points?
  4. Name a covalent substance that conducts electricity.
  5. How many covalent bonds does carbon form in diamond?

Summary 

  • Covalent bonds involve shared pairs of electrons between non-metals
  • Atoms share electrons to get a full outer shell
  • Covalent bonding forms molecules, not ions
  • Simple molecules have low melting points and don’t conduct electricity
  • Giant covalent structures (like diamond) have strong bonds and high melting points